The invention is generally related to data storage subsystems which are accessed via a network, and more particularly to tiered storage.
Enterprise data storage subsystems are used to maintain relatively large data sets. A data storage subsystem includes at least one enterprise storage array which is accessed via a host device. The storage array typically includes multiple physical storage devices, and technologies such as RAID and remote site mirroring may be used to help avoid data loss. Further, tiered levels of storage may be utilized in order to help provide both high performance and high capacity at a practical cost. Applications and devices generally access data in a storage array by sending IOs to the host device. The host device then communicates with the storage array to Read or Write data. If storage resources are organized in hierarchical tiers, data is moved between storage tiers based on IO activity. For example, data may be moved to a lower storage tier as a function of not being accessed for some period of time, or to a higher storage tier as a function of recently being accessed. Generally, data which has been recently accessed is moved to a higher storage tier characterized by faster access time, whereas data that has not been accessed for some period of time may be moved to a lower storage tier characterized by slower access time.